When a cycled battery is charged repeatedly at low rates but not fully charged, the acid is not effectively driven out of the plates, particularly the lower parts, and sulfation results.

Repeated partial charges which do not effect thorough mixing of the electrolyte also result in sulfation. It is difficult in normal battery operation to determine just when sulfation begins, and only by giving periodic equalizing charges and comparing individual cell specific gravity and voltage reading can it be detected in its early stages and corrected or prevented.

Troublesome sulfation does not occur in less than 30 days.

STANDING IN A PARTIALLY OR COMPLETELY DISCHARGED CONDITION

Permitting a battery to stand in a partially discharged condition for long periods allows the sulphate deposited on the plates to harden and the pores to close.

Batteries should be charged as soon as practicable after discharge and not allowed to stand in a completely discharged condition for more than one month. During freezing weather the battery should be recharged immediately following discharge to prevent freezing.

LOW ELECTROLYTE

If the level of the electrolyte is permitted to fall below the tops of the plates the exposed surfaces will harden and become sulphated.

ADDING ACID

If acid is added to a cell in which sulfation exists the condition will be aggravated.

HIGH SPECIFIC GRAVITY

In general, the higher the fully charged specific gravity of a cell the more likely is sulfation to occur and the more difficult to reduce. If in any battery there exists cells having specific gravity more than 0.015 above the average, the possibility of sulfation in these cells will be enhanced.

All cells of a sulphated battery will give low specific gravity and voltage readings. They will not become fully charged after normal charging. An internal inspection will disclose negative plates having a slate like feeling, sulphated negative-plate material being hard and gritty and having a sandy feeling when rubbed between thumb and forefinger.

The internal inspection should be made after a normal charge, since a discharged plate is always somewhat sulphated. A good fully charged negative plate is spongy and springy to the touch and gives a metallic sheen when stroked with the fingernail or knife. A sulphated positive plate is a lighter brown colour than the normal plate.

> Deficit Cycling
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>Modified on: Tue, 26 Aug, 2014 at 4:22 PM
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>Rolls batteries have been designed to provide many cycles and therefore long life. This long life, however, is dependent on the correct charging regime.
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To fully charge a lead acid battery, more ampere hours must be returned to it than have been drawn from it. This is not always possible in Renewable Energy applications as systems may rely solely on the Sun and Wind without backup power (generator/charger). In these instances the battery may not receive a full charge before it is discharged again. If this deficit is not corrected the battery will eventually sulphate and its capacity will deteriorate. To lessen these symptoms it is essential the battery is returned to a fully charged state at least once a month. The battery’s state of charge (SOC) can be checked using a combination of its voltage and specific gravity.
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>If the batteries do not respond to normal charging, a course of equalization* will be required. This is in essence controlled overcharging in order to return the acid back into the electrolyte. Given that the acid is more dense than the water, no noticeable increase in the specific gravity will be noted until the gassing voltage has been reached (2.4VPC) and the two start to diffuse.
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>NOTE: Hydrocaps must be removed during equalization.

The SG quantifies the amount of **Sulfuric Acid** (H<sub>2</sub>SO<sub>4)</sub> to the **water** (H<sub>2</sub>O) in the battery electrolyte. Water has an SG of 1 so anything higher indicates some solvent.

> The next time your batteries don't seem to be taking or holding a charge, check the specific gravity with a hydrometer. If all cells are low even after a long time on charge, chances are you've got some hardened sulfate that has accumulated on the plates. By following the instructions outlined above, the problem may be corrected.
<a href="http://support.rollsbattery.com/support/solutions/articles/5964-battery-sulfation" target="_blank">Rolls Batteries' View</a>

**Lead (Pb) is sulfated** as it takes the place of the Hydrogen (H) atom. So lead becomes <strong> lead sulfate (PbSO<sub>4</sub>)</strong>: <em>Plumbum: Latin</em>

The general level of acid gives the electrolyte an SG of around 1.28 and could well be 1.3

**If the level is high** it would in normal circumstances indicates that the battery is fully charged. However if water has been lost during charging this will also show as an increased SG.

**If the level is low** Hopefully this is part of the normal cyclic sulfation process that occurs as the battery discharges and the SO<sub>4</sub> transfers from the electrolyte to the the lead plates back to the water when charged. Only when the plates have been left discharged for 'quite a while' does the sulfation become difficult to undue and the battery looses capacity, then even with charging the SG stays low.

If despite fears of hardened sulfation it is possible to restore the SG to 1.28 or more then then there is no significantly hardened sulfation.

Longs periods of overcharging are often used to force the sulfate to migrate from the lead plates back to the water. There are other methods such as elctro-vibrations and chemicals that are used, but they are not something I am familiar with.

Thorough and careful attention to the following steps often will restore a sulphated battery to good operation condition.

Clean battery;

Bring electrolyte level to proper height by adding water;

Put battery on charge at the prescribed finishing rate until full ampere-hour capacity has been put into the battery based on the 8 hour rate. If at any time during these procedures the temperature of the battery exceeds 50° C. reduce the charge rate to maintain temperature at or below this point. If any cell gives low readings (0.20 V less than the average cell voltage of the battery), pull and repair the cell before continuing with the procedure;

After full ampere-hour capacity has been put into the battery, continue the charge at the finishing rate until the specific gravity shows no change for a 4 hour period with readings taken hourly. Record voltage and specific gravity readings. Correct specific gravity readings for temperature. These readings indicate the state of charge;

Place battery on discharge at the 8 hour rate and during the test record individual cell voltages and overall battery voltage at the following time intervals: 15 minutes after test is started, then hourly until voltages on one cell reaches 1.80 and from then on at 15 minute intervals. From this point on the cell voltages should be under constant observation and the time recorded when each cell voltage goes below 1.75 volts. Terminate the test discharge when the majority of the cell voltages reach 1.75 volts, but stop the test before any single cell goes into reversal.

If the battery gives rated capacity no further treatment is required other than normal recharge and equalization of gravity.

If the battery does not deliver near-rated capacity, continue the discharge without adjusting the discharge rate until one or more cells reach 1.0 volts.

Recharge the battery at the finishing rate as described above, again charging until there is no further rise in specific gravity over a 4 hour period, readings being taken hourly.

Discharge again at the 8 hour rate and if the battery gives full capacity, recharge and put into service.

If this procedure does not result in full capacity, repeat once more as noted above.

If battery does not respond to this treatment, it is sulphated to the point where it is impractical to attempt further treatment and battery should be replaced.

2 TREATMENT

Thorough and careful attention to the following steps often will restore a sulphated battery to good operation condition using a MMF charger and a Discharger/Analyzer.

Initial Charge Current (I) : 4-5% of the battery capacity,
Constant Voltage (V): 2,4V/cell
Time of charge: from 12 to 24 hours

During the charge process keep under control the battery temperature that must not exceed 50°C.

If any cell gives low readings (0,20 V less than the average cell voltage of the battery), pull and repair the cell before continuing with the procedure.

4. The sulphated batteries have an high internal resistance; when a sulphated battery is put on charge the battery voltage reaches in few time the value of the Constant Voltage set and the charger current is very low.

Continuing to keep the battery on charge for long time with this very low current the lead sulphated is removed by the plates. The battery voltage would tend to decrease but the MMF charger increases the charger current to keep the voltage constant to the value set.

The charge process have to last a long time, from 12 to 24 hours.

If it's possible, keep under control the specific gravity of the electrolyte. If, during the charge the specific gravity doesn't increase for about 4 hours the charge process can be stopped.

After the end of the charge process, record the specific gravity of the electrolyte. The density of the electrolyte indicates the state of the charge.

Place battery on discharge at the 8 hours rate.

If a unit is used to discharge the battery it's advisable to set the discharger with the following parameters:

Discharge Current: 1/8 of the battery capacity
Time of discharge: 8 hours
Final Battery Voltage: 1,70V/cell

The discharger is fully automatics and stops the discharge process if the time of discharge or the minimum battery voltage set are reached. During the discharge, keep under control the individual cell voltages and overall battery voltage at the following time intervals: 15 minutes after test is started, then hourly until voltages on one cell reaches 1.80 and, from then, on at 15 minute intervals. Stop manually the discharge process if the voltage of one of the cell falls below 1,60V .

If the battery, with reference to the discharge parameters set, gives at least the 80% of the rated capacity no further treatment is required other than normal recharge and equalization of gravity.
If the battery does not deliver near-rated capacity, execute a new charge/discharge process.

Again charge the battery for long time between 12 or 24 hours and/or until there is no further rise in specific gravity over a 4 hour period, readings being taken hourly. Keep under control the battery temperature.

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A sulphated battery is one which has been left standing in a discharged condition or undercharged to the point where abnormal lead sulphate has formed on the plates.

When this occurs the chemical reactions within the battery are impeded and loss of capacity result.

This document does not cover all the electricity theory and technology involved in the process of sulfation in battery operated system. For more information, please refer to specialized literature.